Clipper
10-18-2008, 11:52 AM
Diesels ignite the fuel by compression. Ignition starts at about 12:1.
(some boat diesels, Universals for example, actually are designed at 14:1.)
The Powerstrokes and Dodge Cummins run about 18:1, and that's without turbocharging. My Chevy runs 21.5:1.
Since the hydrogen IS a fuel, it is actually igniting sometime during the compression stroke, while the piston is still on its' way up.
This is actually preignition.
I looked up the autoignition temperature of Hydrogen, it is 1085 degrees Fahrenheit, or 585 Centigrade, or 858 degrees Kelvin.
http://www1.eere.energy.gov/hydrogen...fs/fcm01r0.pdf
(page 26)
http://chemistry.about.com/library/w...empconvert.htm
(Temperature conversion calculator.)
Now, using the "Diesel Cycle" calculator in the middle of this page:
http://members.aol.com/engware/calc3.htm
Starting with 1 atmosphere of pressure, in other words, no turbocharging,
858 degrees Kelvin is reached at about 14.17:1 of adiabatic compression.
With turbocharging, it is reached even sooner during the compression stroke.
Now think about this: geometrically, compression not linear, it is progressive.
2:1 compression is reached 50% (1/2) of the way up the compression stroke.
3:1 compression is reached 67% (2/3) of the way up the compression stroke.
4:1 compression is reached 75% (3/4) of the way up the compression stroke.
5:1 compression is reached 80% (4/5) of the way up the compression stroke.
etc...
This, of course, assumes PERFECT valve timing, no fluid flow losses, etc....
(I know, I know, but bear with me, ok?)
14:1 works out to about 93% of the linear movement of the piston. (13/14ths of it's linear stroke.)
93% of linear movement, if my calculations are correct, occurs at about 30 degrees before TDC. (Somebody check me on this, please.)
So 14:1 occurs WAY before the injection event.
And since the hydrogen burns so fast, my guess is that by the time the main fuel injection event occurs, the hydrogen is all burned already.
You ARE, at least, injecting the fuel into a much hotter atmosphere than just pure compression.
But you are NOT burning the hydrogen at the same time as the main fuel charge.
My guess is that this is why diesels do not seem to get as much improvement as gassers.
Subjectively, it seems like the diesel pickup trucks that I've read about seem to get maybe 3-4 mpg gain (max)
on a baseline of 16-18 mpg or so, a gain of about 20-30%.
Gassers seem to be able to pretty consistently achieve 40% to as much as 100% increase.
I have absolutely positively NO evidence of ANY of this...it is pure conjecture,
based on my engineering knowledge, and general (subjective) observations.
But worth thinking about, no?
(some boat diesels, Universals for example, actually are designed at 14:1.)
The Powerstrokes and Dodge Cummins run about 18:1, and that's without turbocharging. My Chevy runs 21.5:1.
Since the hydrogen IS a fuel, it is actually igniting sometime during the compression stroke, while the piston is still on its' way up.
This is actually preignition.
I looked up the autoignition temperature of Hydrogen, it is 1085 degrees Fahrenheit, or 585 Centigrade, or 858 degrees Kelvin.
http://www1.eere.energy.gov/hydrogen...fs/fcm01r0.pdf
(page 26)
http://chemistry.about.com/library/w...empconvert.htm
(Temperature conversion calculator.)
Now, using the "Diesel Cycle" calculator in the middle of this page:
http://members.aol.com/engware/calc3.htm
Starting with 1 atmosphere of pressure, in other words, no turbocharging,
858 degrees Kelvin is reached at about 14.17:1 of adiabatic compression.
With turbocharging, it is reached even sooner during the compression stroke.
Now think about this: geometrically, compression not linear, it is progressive.
2:1 compression is reached 50% (1/2) of the way up the compression stroke.
3:1 compression is reached 67% (2/3) of the way up the compression stroke.
4:1 compression is reached 75% (3/4) of the way up the compression stroke.
5:1 compression is reached 80% (4/5) of the way up the compression stroke.
etc...
This, of course, assumes PERFECT valve timing, no fluid flow losses, etc....
(I know, I know, but bear with me, ok?)
14:1 works out to about 93% of the linear movement of the piston. (13/14ths of it's linear stroke.)
93% of linear movement, if my calculations are correct, occurs at about 30 degrees before TDC. (Somebody check me on this, please.)
So 14:1 occurs WAY before the injection event.
And since the hydrogen burns so fast, my guess is that by the time the main fuel injection event occurs, the hydrogen is all burned already.
You ARE, at least, injecting the fuel into a much hotter atmosphere than just pure compression.
But you are NOT burning the hydrogen at the same time as the main fuel charge.
My guess is that this is why diesels do not seem to get as much improvement as gassers.
Subjectively, it seems like the diesel pickup trucks that I've read about seem to get maybe 3-4 mpg gain (max)
on a baseline of 16-18 mpg or so, a gain of about 20-30%.
Gassers seem to be able to pretty consistently achieve 40% to as much as 100% increase.
I have absolutely positively NO evidence of ANY of this...it is pure conjecture,
based on my engineering knowledge, and general (subjective) observations.
But worth thinking about, no?